Rotary cutting tool with hone edges

ABSTRACT

A rotary cutting tool includes a shaft having and outer surface and having a longitudinal axis, a plurality of helical flutes formed in the shaft about the longitudinal axis, a plurality of helical cutting edges formed at an interface with the outer surface and a respective helical flute about the longitudinal axis, and a plurality of end cutting edges located on an axial distal end of a cutting portion of the shaft, the end cutting edges being contiguous with a corresponding one of the plurality of helical cutting edges and forming a corner in the transition between each of the end cutting edges and the corresponding one of the plurality of helical cutting edges. A hone edge extends along a portion of each of the end cutting edges, the associated corner and a portion of the corresponding one of the plurality of helical cutting edges.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. ProvisionalPatent Application No. 62/014,085 filed Jun. 18, 2014, the contents ofwhich are hereby incorporated in their entirety.

BACKGROUND

This relates in general to rotary cutting tools. One type of knownrotary cutting tool is an end mill, see FIG. 1. End mills typicallyconsist of one or more flutes including a deep helical groove that runsup the cylindrical outer surface of the milling bit. In operation,associated cutting edges may cut a work piece material; together, theflutes and cutting edges—by virtue of rotation of the milling bit—cutaway and remove pieces of the work piece in a manner that creates thedesired form.

One example of a known rotary cutting tool is the Z-Carb® end millmanufactured under U.S. Pat. No. 4,963,059. The U.S. Pat. No. 4,963,059disclosed an end mill having a plurality of paired helical flutesforming an even number of helical peripheral cutting edges equallyspaced circumferentially in one plane wherein the peripheral cuttingedges are formed as a plurality of pairs of diametrically oppositecutting edges having the same helix angle and thereby being symmetricalwith respect to the axis of the body.

End mills peripheral cutting edges remove the bulk of material, but thechip forming process starts near the corner of each edge. Repeatedimpact in this region can be particularly stressful to an end mill andsome form of strengthening is desired.

The corners of carbide end mills can be one the weakest area of such atool, see FIG. 2. The corners of end mills also tend to be the mostvulnerable area, being most susceptible to the onset of chip damage, seeFIG. 3. The increased operating parameters brought about by the everincreasing use of high performance end mill designs has furthered thisconcern. Several methods that have been explored and implemented toprotecting these corners includes a series of grinds, which may becostly and/or difficult to control during manufacturing.

One know simple method of corner strengthening includes a chamfer. Othermore complicated methods includes a corner radius, see FIGS. 4 and 5. Acorner radius will reduce stresses in the areas where applied. Howeverthis method is not sufficient protection for milling most materials.Additional protection methods include a faced hook, see FIGS. 6 and 7 atFH, in which the gashing at the end of the tool is carried out to thecorners. This may significantly increase the strength by making thegeometry more negative, i.e. blunt; however the tradeoff is lostshearing capability and less efficient cutting.

Further methods include the above combined with various gashing methods.A blending grind may be added to the corner radius to further improvefunctionality and smooth the surface transition. A compromise is toblend the end gashing into the fluting to subdue the faced hook. This iscommonly called a “B-Rad” (blend radius), or blend gashing. The downsideis that this blend is difficult to manufacture and some of the negativegeometry still exists, see FIGS. 8 and 9 at BR.

Additionally, portions of all of the above tools still tend to besubject to chipping or other generally undesired damage.

SUMMARY

This relates more specifically to a rotary cutting tool including ashaft having an outer surface and having a longitudinal axis with aplurality of helical flutes formed in the shaft about the longitudinalaxis and a plurality of helical cutting edges formed at an interface ofa respective the helical flutes with the outer surface about thelongitudinal axis

One embodiment includes treating the cutting edges as an improved methodof reducing corner damage and improving performance of solid carbide endmills. One such treatment includes honing at least a portion of thecutting edges. Honing is the action of rounding an otherwise sharpcutting edge so as to remove keenness and thereby toughen the edge forimproved chip resistance. One treatment may include a consistent hone,which encompasses the radial edges, in part of around the entireperiphery, but it is consistent in size, with virtually no variation.

The treatment may include varying hone, varying the hone size accordingto location along the cutting edge or around the periphery. In oneexample, there is hone applied to the radial edges and a relativelyheavier hone applied to areas requiring additional toughness, such asthe corner radii.

It is expected that this varying hone will result in less cornerchipping. In one instance, the application of the varying hone may beachieved through the use of a computer controlled brush honing machine,which provides the control required to change hone size. Such a machinemay be further enhanced by flanging the normally loose filament brush soas to better localize the filament, resulting in a more precise honingprocess.

Testing of the varying hone shows that not only are the corner radiisufficiently more protected, cutting force and torque are reduced, andradial edge condition is improved, as compared to other methods forreducing corner chipping.

In at least one embodiment, a rotary cutting tool includes a shafthaving and outer surface and having a longitudinal axis, a plurality ofhelical flutes formed in the shaft about the longitudinal axis, aplurality of helical cutting edges formed at an interface with the outersurface and a respective helical flute about the longitudinal axis, anda plurality of end cutting edges located on an axial distal end of acutting portion of the shaft, the end cutting edges being contiguouswith a corresponding one of the plurality of helical cutting edges andforming a corner in the transition between each of the end cutting edgesand the corresponding one of the plurality of helical cutting edges. Ahone edge extends along a portion of each of the end cutting edges, theassociated corner and a portion of the corresponding one of theplurality of helical cutting edges.

Various aspects will become apparent to those skilled in the art fromthe following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a known end mill.

FIG. 2 is an enlarged portion of the end mill of FIG. 1.

FIG. 3 is a view similar to FIG. 2 except showing the end will aftersignificant wear. and show new and used corners.

FIG. 4 is a tangential view of a portion of an end mill with cornerradius.

FIG. 5 is a side of the portion of the end mill of FIG. 4.

FIG. 6 is a tangential view of a portion of an end mill with faced hook.

FIG. 7 is a side of the portion of the end mill of FIG. 4.

FIG. 8 is a tangential view of a portion of an end mill with B-Rad.

FIG. 9 is a side of the portion of the end mill of FIG. 4.

FIG. 10 is an enlarged front view of a portion of an end mill with honeedges.

FIG. 11 is a further enlarged portion of FIG. 10.

FIG. 12 is a tangential view the end mill of FIG. 10.

FIG. 13 is a side view of the end mill of FIG. 10.

FIG. 14 is an enlarged perspective view of the hone edge of the end millof FIG. 10.

FIG. 15 is a schematic illustration of a first hone edge.

FIG. 16 is a schematic illustration of a second hone edge.

FIG. 17 is a schematic illustration of a third hone edge.

FIG. 18 is a schematic illustration of a fourth hone edge.

FIG. 19 is a schematic illustration of a fifth hone edge.

FIG. 20 is an enlarged view of a cutting edge of a conventional end millafter use.

FIG. 21 is an enlarged view of a cutting edge of an end mill with honeedge after use.

FIG. 22 is a front view of a portion of a CNC machine including a chuckholding a shaft.

FIG. 23 is a front view of another portion of the CNC machine of FIG. 22including a machine brush.

FIG. 24 is a perspective view of the brush of FIG. 23.

FIG. 25 is another perspective view of the CNC machine of FIGS. 22-24showing the machine in operation.

FIG. 26 is a further perspective view of the CNC machine of FIGS. 22-24showing the machine in further operation.

FIG. 27 shows an end mill with B-Rad.

FIG. 28 shows an end mill with hone edge.

DETAILED DESCRIPTION

There is shown in FIGS. 10-14, 21 and 28 an end mill rotary cutting tool110. The tool 110 includes a shaft 112 having and an outer surface 114and having a longitudinal axis X. The shaft 112 includes a shank portion116, see FIG. 22, and cutting portion 118. A plurality of helical flutes120 are formed in the shaft 112 in the cutting portion 118 about thelongitudinal axis X.

A plurality of helical cutting edges 122 are formed at an interface withthe outer surface 114 and a respective helical flute 120 about thelongitudinal axis X. A plurality of end cutting edges 124 are located onan axial distal end 126 of the cutting portion 118 of the shaft 112. Theend cutting edges 124 are contiguous with a corresponding one of theplurality of helical cutting edges 122 and form a corner 128 in thetransition between each of the end cutting edges 124 and thecorresponding one of the plurality of helical cutting edges 122.

A hone edge 130 extends along a portion of each of the end cutting edges124, the associated corner 128 and a portion of the corresponding one ofthe plurality of helical cutting edges 122.

The hone edges 130 may all be varying hone edges, that is to say thatthe amount of honing may vary along the length of the edge. The varyinghone edges 130 may, for example, increase from the associated helicalcutting edge 122 toward the associated end cutting edge 124. There maybe increased honing on the corners 128 as compared to the helicalcutting edges 122 or as compared to the end cutting edges 124 or both.The hone edges 130 may be formed to all be geometrically positive.

The end mill of claim 2 where the helix angle of the helical flutesvaries along the longitudinal axis.

The rake angle of the helical cutting edges 122 may vary along thelongitudinal axis X.

There is illustrated in FIGS. 15-19 a variety of hone edge with thethickness of the hone line 132 indicating the amount of honing bylocation.

In one embodiment, edges are rounded with a diamond impregnated fiberbrush. Upon testing, see the method of corner strengthening has producedsignificant results. The corner radius stronger, as compared to othermethods, and cutting force and torque were lower, and overall toolcondition was better.

This method may include that the treatment size would not be consistentover the entire edge length. For example, it may vary so as to provideprotection according to the load associated with a specific location onan end mill, or vary in any other way as desired. As an example, theaxial edges may receive 0.001-0.002 (inch) radius, transitioning aroundthe corner radius to 0.0003-0.0005 (inch) on the radial edges.

Listed are some of the benefits discovered provided by varying edgetreatment as compared to other edge treatments: reduction of maximumforce by 13.8% and torque by 11.5%, improvement of chip resistance atthe corners over conventional protection methods, and improvement ofchip resistance along the radial cutting edge.

In one embodiment this may be combine with varying helix and/or varyingrake to create a tool where the combination of two or three worktogether. It is expected that the varying rake/varying helix will reducevibration, while the varying hone may be able to withstand morevibration. It is expected that when combined these features will createa highly chip resistant design.

Illustrated is a test that compares a standard Z-Carb AP manufacturedwith a B-Rad, see FIGS. 20 and 27, to the identical product manufacturedwithout a B-Rad, but with an axial edge treatment (hone) of 0.001(inch), see FIGS. 21 and 28.

Profile cuts were made in 4140 and 316 stainless at Tool Wizardparameters. Parameters for Test 085-09 were duplicated, which was a testthat had shown the comparison between a B-Rad and a conventionalunprotected corner radius. In the 4140 profile test, the stockroomsample (T1) showed micro-chipping, as typically observed during acoating test. T2, without the B-Rad but with the axial hone, did notshow this edge condition. Neither tool showed any notable corner radiusarea damage. In Test 2, profile milling in 316 stainless, the stockroomsample (T3) showed edge chipping which was not exhibited by T4, thenon-B-Rad/axial honed tool. Neither tool showed any corner damage. Test3 involved profile milling in 15-5 PH stainless and after milling 1600inches both tools (T5 and T6) had identical wear and chipping and nocorner radius area damage. Test 4 used the load cell to determine toolload while plunging. Each tool was plunged into the 4140 workpiece threetimes and the forces measured, recorded and averaged. Tool 8 with noB-Rad and the axial hone averaged 14 percent less maximum Z-axis forceand 12 percent less maximum torque than the stockroom sample (T7).

In summary, in these tests, the stockroom samples showed edge damageequal to or worse than the axial honed tools, as well as generating moreZ-axis force and torque while plunging. Overall, the preliminary resultssuggest the axial edge treatment is not detrimental to performance, andis likely beneficial to reduce corner damage as compared to thenon-axial honed tools.

Below are Tables representing Test 1-Test 4 that illustrate four testsof stock sample compared to a honed sample.

Tool Wizard parameters (Test 1)¤ ¤ MACHINE¤ TOOL HOLDER¤ COOLANT¤ 4140alloy steel 28HRc¤ Haas VM3¤ Techniks ER-32 short¤ S-373¤ SPEED¤ FEED¤RADIAL WIDTH¤ AXIAL DEPTH¤ 2.865 rpm/375 sfm¤ 26.24 ipm/.00229 ipt¤ 250″(50% D)¤ 500″ (D)¤ TOOL¶ TYPE¶ TRIN¶ NO.¤ DESCRIPTION¤ MACHINE¤ USAGE¤INSPECTION NOTES¤ 1¤ ZAP1C05000_030TX stockroom .0003″¤ 640″¤ Varyingmicro chipping on cutting edges and corner radii. ¤ sample¤ 2¤ Testsample without B-Rad; .001″ axial .0004″¤ 640″¤ Even and consistent oncutting edges and corner radii¤ hone.¤

Tool Wizard parameters (Test 2)¤ WORKPIECE¤ MACHINE¤ TOOL HOLDER¤COOLANT¤ 316 stainless¤ Haas VM3¤ Techniks ER-32 short¤ S-373¤ SPEED¤FEED¤ RADIAL WIDTH¤ AXIAL DEPTH¤ 3.025 rpm/396 sfm¤ 21.78 ipm/0018 ipt¤250″ (50% D)¤ 400′ (80% D)¤ TOOL¶ TYPE¶ TRIN¶ NO.¤ DESCRIPTION¤ MACHINE¤USAGE¤ INSPECTION NOTES¤ 3¤ ZAP1C05000_030TX stockroom .0003″¤ 640″¤Varying edge damage with chipping .0044″ to .007″ on primary sample¤Corners/B-Rad intact¤ 4¤ Test sample without B-Rad; .001″ axial .0002″¤640″¤ .0008″ edge wear, even and consistent on cutting edges and cornerradii¤ hone.¤

Parameters from test 085-09 (Test 3)¤ WORKPIECE¤ MACHINE¤ TOOL HOLDER¤COOLANT¤ 15-5 PH stainless¶ Haas VM3¤ Techniks ER-32 short¤ S-373¤ 35/37HRc¤ SPEED¤ FEED¤ RADIAL WIDTH¤ AXIAL DEPTH¤ 2.180 rpm/285 sfm¤ 17.0ipm/.0019 ipt¤ 250″¤ .125″¤ TOOL¶ TYPE¶ TRIIN¶ NO.¤ DESCRIPTION¤MACHINE¤ USAGE¤ INSPECTION NOTES¤ 5¤ ZAP1C05000_030TX stockroom .0002″¤1120″¤ .0025″ wear, not tool damage¤ sample¤ 1600″¤ .0032″ wear, eachflute has a small chip on edge. No corner area damage¤ 6¤ Test samplewithout B-Rad; .001″ axial .0004″¤ 1120″¤ .0025″ wear, no tool damage.¤hone.¤ 1600″¤ .0033″ wear, each flute has a small chip on edge No cornerarea damage.¤

Plunge in load cell (Test 4)¤ WORKPIECE¤ MACHINE¤ TOOL HOLDER¤ COOLANT¤4140 alloy steel 28HRc¤ Haas VM3¤ Techniks ER-32 short S-373¤ SPEED¤FEED¤ RADIAL WIDTH¤ AXIAL DEPTH¤ 2.865 rpm/375 sfm¤ 13.0 ipm/.0045 ipr¤500″ (D)¤ .050″¤ TOOL¶ TYPE¶ TRIN¶ NO.¤ DESCRIPTION¤ MACHINE¤ USAGE¤INSPECTION NOTES¤ 7 ZAP1C05000_030TX stockroom .0003″¤ 3 plunges¤ 328.14lbs average maximum Z-axis load. 69.1 average in lbs torque¤ sample¤ 8Test sample without B-Rad; .001″ axial .0003″¤ 3 plunges¤ 282.89 lbsaverage maximum Z-axis load. 61.1 average in lbs torque¤ hone,¤Comments: Tool 8 has approximately 14% less average Z-axis load and 12%less average torque requirement (maxiumuns) ¤

Below are Tables Tool 7 and Tool 8 that give the parameters for thestock sample and honed sample, Plunges 1-3.

Tool 7 stockroom sample¤ Plunge 1¤ Plunge 2¤ Plunge 3¤ UNITS→“lbs”¶UNITS→“lbs”¶ UNITS→“lbs”¶ MEAN→ 265.72¶ MEAN→ 265.85¶ MEAN→ 275.03¶ STDDEV. → −50.05¶ STD DEV. → −54.32¶ STD DEV. → −66.14¶ MINIMUM → 104.80¶MINIMUM → 117.05¶ MINIMUM → −70.62¶ MEDIAN → 282.62¶ MEDIAN → 284.24¶MEDIAN → 291.65¶ MAXIMUM → 315.67¶ MAXIMUM → 315.67¶ MAXIMUM → 353.08¶ ¤¤ ¤ UNITS→“inlb”¶ UNITS→“inlb”¶ UNITS→“inlb”¶ MEAN→ 52.211¶ MEAN→50.895¶ MEAN→ 50.236¶ STD DEV. → 11.651¶ STD DEV. → 15.633¶ STD DEV. →15.741¶ MINIMUM → 19.342¶ MINIMUM → −5.120¶ MINIMUM → −6.827¶ MEDIAN →54.233¶ MEDIAN → 54.327¶ MEDIAN → 52.716¶ MAXIMUM → 66.274¶ MAXIMUM →71.204¶ MAXIMUM → 69.687¶ ¤ ¤ ¤.

Tool 8 without B-Rad and .001 axial edge prep/hone¤ Plunge 1¤ Plunge 2¤Plunge 3¤ UNITS→“lbs”¶ UNITS→“lbs”¶ UNITS→“lbs”¶ MEAN→ 238.00¶ MEAN→244.21¶ MEAN→ 248.13¶ STD DEV. → −15.09¶ STD DEV. → −20.69¶ STD DEV. →−38.18¶ MINIMUM → 205.42¶ MINIMUM → 184.60¶ MINIMUM → 119.71¶ MEDIAN →239.90¶ MEDIAN → 247.55¶ MEDIAN → 253.56¶ MAXIMUM → 261.21¶ MAXIMUM →267.55¶ MAXIMUM → 319.92¶ ¤ ¤ ¤ UNITS→“inlb”¶ UNITS→“inlb”¶UNITS→“inlb”¶ MEAN→ 46.779¶ MEAN→ 47.885¶ MEAN→ 48.260¶ STD DEV. →−7.386¶ STD DEV. → −7.835¶ STD DEV. → 13.354¶ MINIMUM → 22.394¶ MINIMUM→ 20.964¶ MINIMUM → −7.433¶ MEDIAN → 49.076¶ MEDIAN → 49.409¶ MEDIAN →48.028¶ MAXIMUM → 55.175¶ MAXIMUM → 57.938¶ MAXIMUM → 70.136¶ ¤ ¤ ¤.

The developed method addresses the corner strength issue while alsomaintaining efficient shearing capability. By utilizing a CNC brushhoning machine, method has been crafted to utilize brush wheel of thehone machine to produce a relatively wider, heavier hone at the axialend of the tool which diminishes in size as it proceeds down the radialside of the flutes.

By eliminating the faced hook and B-Rad, the shearing capability isimproved and by adding the variable hone the corners are protected.

One method of forming a rotary cutting tool includes the steps of:

providing a shaft having and outer surface and having a longitudinalaxis;

forming a plurality of helical flutes in the shaft about thelongitudinal axis defining a cutting portion, the remainder of the shaftdefining a shank portion;

forming a plurality of helical cutting edges at an interface with theouter surface and a respective helical flute about the longitudinalaxis;

-   -   forming a plurality of end cutting edges on an axial distal end        of cutting portion of the shaft, the end cutting edges being        contiguous with a corresponding one of the plurality of helical        cutting edges and forming a corner in the transition between        each of the end cutting edges and the corresponding one of the        plurality of helical cutting edges; and

forming a hone edge extending along a portion of each of the end cuttingedges, the associated corner and a portion of the corresponding one ofthe plurality of helical cutting edges.

Referring to FIGS. 22-26, the shaft may be secured in chuck at the shankportion and then rotated. A machining brush may be provided and appliedto the helical cutting edges, the corners, and/or the end cutting edgesto form hone edges, such as varying hone edges. The brush may includefilaments flanged between two disks. This may be performed by a CNCmachine.

While principles and modes of operation have been explained andillustrated with regard to particular embodiments, it must beunderstood, however, that this may be practiced otherwise than asspecifically explained and illustrated without departing from its spiritor scope.

What is claimed is:
 1. An end mill rotary cutting tool comprising: ashaft having and outer surface and having a longitudinal axis, the shaftincluding a shank portion and cutting portion; a plurality of helicalflutes formed in the shaft in the cutting portion about the longitudinalaxis; and a plurality of helical cutting edges formed at an interfacewith the outer surface and a respective helical flute about thelongitudinal axis; a plurality of end cutting edges located on an axialdistal end of cutting portion of the shaft, the end cutting edges beingcontiguous with a corresponding one of the plurality of helical cuttingedges and forming a corner in the transition between each of the endcutting edges and the corresponding one of the plurality of helicalcutting edges; and a hone edge extending along a portion of each of theend cutting edges, the associated corner and a portion of thecorresponding one of the plurality of helical cutting edges.
 2. The endmill of claim 1 where the hone edges are all varying hone edges.
 3. Theend mill of claim 2 where the varying hone edges increase from theassociated helical cutting edge toward the associated end cutting edge.4. The end mill of claim 2 where the helix angle of the helical flutesvaries along the longitudinal axis.
 5. The end mill of claim 2 where therake angle of the helical cutting edges varies along the longitudinalaxis.
 6. The end mill of claim 2 where there is increased honing on thecorners as compared to the helical cutting edges.
 7. The end mill ofclaim 2 where there is increased honing on the corners as compared tothe end cutting edges and the helical cutting edges.
 8. The end mill ofclaim 2 where the hone edges are all geometrically positive.
 9. A methodof forming a rotary cutting tool comprising: providing a shaft havingand outer surface and having a longitudinal axis forming a plurality ofhelical flutes in the shaft about the longitudinal axis defining acutting portion, the remainder of the shaft defining a shank portion;forming a plurality of helical cutting edges at an interface with theouter surface and a respective helical flute about the longitudinalaxis; forming a plurality of end cutting edges on an axial distal end ofcutting portion of the shaft, the end cutting edges being contiguouswith a corresponding one of the plurality of helical cutting edges andforming a corner in the transition between each of the end cutting edgesand the corresponding one of the plurality of helical cutting edges; andforming a hone edge extending along a portion of each of the end cuttingedges, the associated corner and a portion of the corresponding one ofthe plurality of helical cutting edges.
 10. The method of claim 9further comprising, prior to forming the hone edges, securing the shaftin chuck at the shank portion.
 11. The method of claim 10 where theforming the hone edges includes rotating the shaft by the chuck.
 12. Themethod of claim 9 further comprising, providing a machining brush, andwhere in the forming the hone edges includes applying the brush to thehelical cutting edges.
 13. The method of claim 9 where the brushincludes filaments flanged between two disks.
 14. The Method of claim 9further comprising, providing a machining brush, and where in theforming the hone edges includes applying the brush to the end cuttingedges.
 15. The method of claim 14 where the brush includes filamentsflanged between two disks.
 16. The method of claim 11 where the honeedges are varying hone edges.
 17. The method of claim 16 where thevarying hone edges increase from the associated helical cutting edgetoward the associated end cutting edge.
 18. The method of claim 16 wherethere is increased honing on the corners as compared to the helicalcutting edges.
 19. The method of claim 9 where the forming hone edges isperformed by a CNC machine.